In cross country or touring skiing, the ski boot of the skier is typically attached in a rotatable manner to the ski. Often the ski boot will be provided with a pin, or the like, at the front portion thereof, which fits in an appropriately shaped housing section on the binding or mounting plate attached to the ski. The action of cross country skiing involves the skier removing the heel section of the boot from the top surface of the ski whilst performing the walking type manoeuvre. In order to increase the effectiveness of cross country skiing, it is common to provide some sort of restorative flexor in the region of the toe portion of the ski boot. This flexor acts to counter the rotation of the ski boot where the heel leaves the top surface of the ski, such that the heel of the ski boot will tend to be pushed back into contact with the top surface of the ski.
Numerous prior art flexors have been proposed, the most simple being a compression flexor formed by some elastic-type material. This sort of flexor fits in front of the toe portion of the boot of the skier, and will simply be compressed when the skier rotates the ski boot and brings the heel of this boot off the top surface of the ski. Looking at FIG. 6a, a graph is provided showing the force versus the displacement curves for a variety of possible flexors. As shown in this diagram, the amount of force required (shown in the Y-axis) is depicted for a certain degree of rotation of the ski boot. The graph shown by the dotted line, describes the case of a fully compression-type flexor. As can be seen from this graph, an approximately exponential relationship starting from no rotation to a maximum rotation is obtained, which is understandable as clearly a compressed flexor can only be compressed so far. Further, the act of compressing the flexor will lead to increasing forces required for the same compression amount, thus giving the approximately exponential curve. The values shown for each curve in FIG. 6a are generally accepted values, and are indeed preferred values insofar as they relate to the flexor of the present disclosure, as detailed below. These values are not, however, considered to be a fully restrictive disclosure, and indeed equally useful characteristics for a flexor can be obtained with values lying anywhere between 30% either side of these given examples.
A second curve is given, formed by the dot-dash line, which comprises essentially two straight lines for the force versus displacement curve. In this case, a spring-type element is attached to a rigid flexor, and this spring resists the rotation of the ski boot. Most springs act in a linear manner in this way, thus leading to an approximately linear force versus displacement section to the graph. Clearly, once the spring has reached its maximum compression or the rotatable flexor arm has reached the point where its lower surface is in contact with the mounting plate or ski binding, a discontinuity in the linear curve is generated. At this point, the only further possibility is some degree of compression of either the toe in the ski boot, the compression of the flexor itself or some degree of deformation of the flexor and ski binding. This leads to a very steep gradient in the force versus displacement curve, and is essentially a result of the flexor arm being unable to rotate further because of the binding or the like.
In each of these cases, drawbacks exist. For example, in the simple compression flexor, it is quite clear that the maximum rotation is limited by the literal maximum amount of compression that the flexor can accommodate. This is rarely reached, however, as the skier is then providing a large force on the flexor in order to obtain the desired rotation and compression, which will become extremely painful after a short time. In reality, the maximum amount of boot rotation which can be achieved by means of a simple compression flexor, is between 20° and 25°. In order to increase the amount of rotation of the boot, the flexor must be structured such that it can be compressed to a greater degree. In order to achieve this, however, the return force generated by the flexor will generally be reduced at lower rotation angles, which is undesirable from the point of the skier.
With regard to the spring option, whilst this gives a tuneable force versus displacement curve in the linear portion, the sudden discontinuity is a jarring force felt by the skier, in particular in their toes, which is uncomfortable and undesirable for the skier. Additionally, the lack of feedback at the high rotation angles of the ski boot, i.e. the fact that the high rotation angles do not give rise to high resistive forces, leads to the skier feeling disconnected from the ski and snow. This lack of connection is quite disorienting for skiers used to such feedback, and is an undesirable aspect which needs considering.
It is most desirable to have a combination of these two curves, wherein the first section of the force versus rotation curve is a generally linear curve, and wherein the amount of return force for a certain boot rotation can be tailored. Once a chosen maximum rotation has been obtained, it is further desirable to avoid a sudden discontinuity, and give a smooth transition into an exponential type of force versus displacement curve.
The advantages associated with this sort of force versus displacement curve relate to being able to accommodate a much larger rotation angle of the boot with regard to the ski. In particular, a larger rotation angle of the boot will allow the skier to make a longer stride, thus improving the technique and efficiency of the skiing action. Additionally, this longer stride can be undertaken without fear of digging the nose of the ski into the snow. As the larger rotation angle is not associated with a larger force applied through the boot by the skier onto the ski, there is no chance of the nose of the ski being forced into the snow. A further advantageous aspect, is that the skier still feels well connected with the ski and snow, which is a result of the final higher return force acting on the boot at the high end rotation point. Finally, as the force being applied to the ski boot will generally be lower, the skier will not suffer excessive force on the toes, which will tend to reduce any bruising which is typical for long periods of cross country skiing.